This invention relates generally to welding machines and more particularly to a seamer with improved back-up assembly for seam welding together workpiece plates of the same thickness or plates of different thickness and for facilitating removal and changing of back-up bars.
Welding techniques join workpiece plates by the application of heat and/or pressure, with or without the addition of a filler metal, and may be roughly divided into two classes, namely pressure welding and fusion welding. Seam welding is a process of closing a seam between two workpieces by a continuous resistance weld formed between two electrodes. The expansion and contraction of workpieces as they are heated by the welding must be allowed for, and jigs or clamps designed to hold the parts in correct alignment during welding.
It is well known and shown in U.S. Pat. No. 3,122,118 that a clamping device such as multiple paddles or fingers (usually aluminum) can be used to apply pressure continuously downward and a back-up bar lodged in a groove provided in the table of the seamer can be used to apply pressure continuously upward to hold the workpieces in correct alignment. By utilizing the back-up bar in conjunction with the clamping fingers, the tolerance after welding can normally be reduced since the table and the back-up bar provide a levelling means for the workpiece plates.
When two plates of equal thickness are welded together, the back-up bar is generally flat-sided with one side supporting the two workpieces in a level plane. In conventional welding operations, when the workpiece plates are of different thickness, the flat back-up bar supports the bottom of the two plates so that the plates are in a level plane on the underside and are uneven on the upperside where the plates are welded, resulting in a weaker and less accurate seam.
One problem with conventional back-up bar assemblies is that there is not effective surface contact between the back-up bar and workpiece plates providing continuous upward pressure responsive to the downward pressure of the clamping fingers, when the workpiece plates are of different thickness, and it is desired to seam the plates with the upperside in a level plane. The seamer operator is unable to adapt the back-up bar to each configuration of two workpieces of unequal thickness, especially when each welding operation consists of two workpieces of different thicknesses than the prior operation's two workpieces.
As shown in U.S. Pat. No. 3,122,118, the conventional back-up bar assembly consists of a slot formed in the top of the work table with the slot extending longitudinally from end to end of the table along the center longitudinal axis. Slidably interfitted in the slot is a back-up bar having a top surface that lies flush with the top surface of the work table and providing a welding zone extending endwise of the table. When a new back-up bar, a differently configured back-up bar or a back-up bar of a different material is desired, there is considerable down time and wasted man hours during the difficult and time consuming process of dislodging the old back-up bar from the seamer and replacing it with another.
There is no known prior art assembly that allows the back-up bar and holder to be quickly removed from the seamer and a new back-up bar and holder slid into the seamer so that the old back-up bar can be removed from the old holder while the new back-up bar and holder are being utilized in a seaming operation.
Prior art seamer and back-up bar assemblies require many man hours per unit, increased changeover time and additional work in the weld operation to weld workpiece plates of different thickness and to change back-up bars.
The present system seamer with improved back-up bar assembly overcomes these and other disadvantages in a manner not revealed in the known prior art.